The preferred embodiment relates to a method and system for function testing a valve particularly a safety valve, such as a globe valve, a butterfly valve, a ball cook valve or the like, in a process engineering plant, such as a petrochemical plant.
In one such method and with one such system a test is made to check whether the safety valve is capable of assuming from its so-called normal position as an either fully closed or fully open position in a certain operating situation, such as in an emergency situation to run the plant, to a predetermined final position such as, for example, a fully closed or fully open final position. The problem generally involved in such function testing is that closing the safety valve greatly detriments normal operation of the plant, it not seldom being necessary that the complete plant needs to be shut down to function test the safety valve.
It is known in implementing function testing of the safety valve to provide a bypass valve in parallel arranged in a line bypassing the safety valve. In normal operation of the plant the bypass valve is positioned idle, which is normally closed.
In function testing, the bypass valve is positioned to a test position. The sequence in stepping the method through function testing is specified, for example in ISA-TR96.05.01/2000 as follows: the bypass valve is first to be fully opened; then the safety valve is to be closed, for example by deactivating a solenoid valve which controls a pneumatic actuator positioning the safety valve; by means of a position sensor a test is then made as to whether the safety valve really has assumed the desired closed position; after this, the safety valve is to be reopened and it is sensed by the position sensor whether the safety valve returns to its fully open position; the bypass valve is then to be closed; and the closed position is then to be sensed by a corresponding position sensor assigned to the bypass valve.
With the safety valve open and the bypass valve closed normal operation of the plant is re-attained.
One drawback of this known function testing method is that parameters important for demonstrating proper functioning such as leakage and closing rate of the safety valve cannot be sensed without direct mechanical access to the valve.
Known from EP 0 284 785 A1 is a method of a leak-detection (tightness testing) device for two valves arranged in line in a fluid conduit.
It is an object to define a method and an assembly for function testing a safety valve with which an indication as to leakage or closing rate of the safety valve can now be obtained without detrimenting operation of the plant.
In a method or system for function testing of a safety valve in a process engineering plant, it is tested whether the safety valve travels from a normal position to a predetermined final position in a certain operating situation of the plant. A bypass valve bypasses the safety valve and assumes an idle position in a normal operation of the plant and a predetermined test position for function testing of the safety valve. The test position of the bypass valve is established such that a predetermined fluid flow through the bypass valve is permitted.